Ndro and associative memory



Feb. 3, 1970 A. J. KOLK, JR

NDRO AND ASSOCIAT IVE MEMQRY 2 Sheets-Shget 1 Original Filed June 16,1964 'Feb. 3, 1970 A. J. KOLK, JR 3,493,944

NDRO, AND ASSOC IATIVE MEMORY Original Filed June 16, 1964 2Sheets-Sheet 2 Mam United States Patent Office 3,493,944 Patented Feb.3, 1970 3,493,944 NDRO AND ASSOCIATIVE MEMORY Anthony J. Kolk, Jr.,Rolling Hills, Calif., assignor to Litton Systems, Inc., Woodland Hills,Calif. Continuation of application Ser. No. 375,575, June 16, 1964. Thisapplication Jan. 2, 1969, Ser. No. 791,858 Int. Cl. Gllb 5/62 US. Cl.340174 9 Claims ABSTRACT OF THE DISCLOSURE A magnetic memory elementwhich comprises two or more hollow cylinder-like structures of magneticmaterial having closed circumferential fiux paths therein and having thetop and bottom edges joined, respectively, by magnetic material to forma closed flux path angularly oriented to the circumferential flux paths.A bias circuit is so coupled to the memory element as to apply amagnetic field to the angularly oriented flux path. A write circuit forSetting the flux orientation into either a first or a secondcircumferential remanent magnetic state is coupled to thecircumferential flux paths; an interrogation circuit is provided fortemporarily applying a magnetic field in a selected one of thecircumferential directions; and a sensing circuit is coupled to theangularly oriented flux path for sensing a change in flux during theapplication of the interrogation field.

This is a continuation of US. patent application Ser. No. 375,575, filedJune 16, 1964 now abandoned.

This invention relates in general to magnetic storage or memory arraysand in particular to new and improved plated magnetic memory elementsand the techniques and methods of construction thereof.

Great emphasis has recently been placed on the design and constructionof storage or memory arrays for use in high speed computers. Because ofthe myriad of uses to which the computers have been placed, variousconsiderations have dictated the type of memory elements to be used. Asit has been found that computers function most accurately when theinformation is in the form of a zero or a one, that is when there iseither a signal or no signal, various bistable elements have logicallyfound favor as suitable for storage elements; there are elements whichexist in one of two stable states and can be switched from one state tothe other by the application of a voltage or a magnetic field. Amongsome of the requirements for these storage elements are low drive orpower consumption, high switching speed, high information or bitdensity, low cost per element, uniformity and reliability, strength ofthe output signal, and good heat transfer to prevent a degradation inthe quality of the output signal. One of the most widely used elementsis the ferrite core composed of a powdered, compressed, and sinteredmagnetic material having high resistivity and consisting chiefly offerric oxide combined with one or more other metal oxides. While ferritecores have low drive and power consumption and produce sufficientlystrong output signals, they are limited in their switching speed andtheir high temperature operation (due to poor heat transfer). Since theyare individually molded, there are wide variations in uniformity; inaddition, since they must be assembled into memory planes andindividually wired, they have a low bit density and high bit cost in thefabricated memory. Although some of the wiring problems have beenalleviated by placing the ferrite cores into holes in a substrate andusing printed wiring over the substrate and through the holes, the basicdisadvantages of individual molding and assembly still remain.

Since ferrite cores have these limitations, investigations.

have been made in evaporated and plated magnetic thin films. These filmsmay be constructed with an easy direction of magnetization along whichthe magnetization vectors of the film tend to align to bring the energyof the film to its lowest state; such a magnetic film is calledanisotropic and the excess energy required to align the magnetizationvectors in the hard direction of magnetization, that is the directionorthogonal to the easy direction of magnetization, is called theanisotropy energy. Since an anisotropic magnetic film may be veryquickly switched by utilizing a magnetic field which is antiparallel tothe direction of magnetization of the film coupled with a magnetic fielddirected along the hard direction of magnetization, that is anorthogonal magnetic field, to rotate the magnetization vectors in theplane of the film (called rotational switching), these films areinherently high speed devices. Because of their thinness and the massapplication techniques utilized, they are potentially capable ofproviding high bit density and low bit cost accompanied by inherentuniformity. Since, however, magnetic poles have not been found to existindividually but only in pairs of opposite polarity, any magnetic fieldgenerated by a magnetic material must close back upon itself; this isusually accomplished, as in the case of a magnet, by the magnetic pathgoing through the magnetic material and across the pole gaps of themagnet to form a closed flux path. In the case of a uniformly alignedmagnetic thin film, the magnetic path goes through the film, out fromone edge and across the surface of the film (externally), and back inthe other edge; this external magnetic field is termed the demagnetizingfield of the magnetic film. Since this demagnetizing field isantiparallel to the magnetization of the film, it tries to reverse themagnetization vectors of the film itself resulting in a decrease ofthreshold or slowing of the hysteresis loop of the magnetic film;because of this decrease in threshold the magnetization vectors do notrapidly switch at a predetermined magnetic field, and a lower signaloutput is ob tained accompanied by a high amount of noise. If the memoryarray is composed of a matrix of magnetic dots on a planar substrate,the tendency exists for a large amount of cross-talk due to the magneticinteraction between spots caused by the open flux path and the externalmagnetic field. If the magnetic memory consists of a thin film havingregions of oppositely directed magnetization therein the boundaries(domain walls) between the oppositely oriented regions (magneticdomains) are subject to creep and walking because of the tendency of theboundaries to move to a position where the magnetic energy of the filmis in its lowest state, the high energy condition existing because ofthe open flux nature of the magnetic film. In addition, the magneticfilm has a low signal output due both to the small amount of magneticmaterial involved and the poor flux coupling of the magnetic film with asense line. While some of these problems have been solved to a limiteddegree by the use of a pair of magnetic films to partially close theopen flux path or by forming holes with closed flux paths in a planarsubstrate by the molding and plating of an orthogonal matrix of plasticcylinders whose axes of revolution lie in the plane of the substrate,other problems have arisen. Some of these are the lowering of bitdensity, proper placement of individual holes in a hole pattern, properregistration of two dot-type memory planes, and fabrication ofsubstrates suitable for the deposition of magnetic material with desiredcharacteristics, since the techniques of molding, punching, or drillingof holes have not provided suificient control of size, uniformity, orsurface characteristics.

It is therefore the primary object of the present invention to providean improved magnetic memory array along with a method of constructionthereof suitable for use with micro-electronic and integratedsemiconductor circuitry.

It is another object of the invention to describe a new and improvedmagnetic memory element having a closed flux path and capable of beingmass fabricated with loW bit cost and high uniformity.

It is a further object of the invention to provide an improved magneticmemory array having high bit density and low power consumption.

It is still another object of the invention to introduce magnetic memoryelements suitable for use in data processing systems having fastswitching speeds, good heat transfer, and capable of providing strongoutput signals.

Generally speaking, in this invention a matrix of holes having smoothwalls is formed in a preselected substrate. The entire substrate and, inparticular, the walls of the holes are then successively plated with oneor more layers of an electrically conductive material and a layer ofmagnetic material. Portions of the layers are then selectively removedto leave a matrix of plated magnetic toroids; these toroids may beisolated, or selectively joined by magnetic material. One or more layersof insulated conducting leads are then plated across the substrate andthrough the plated magnetic toroids to form intimately coupled write,interrogate, and sensing patterns.

The invention and its objects, together with further features andadvantages thereof, will become more apparent with reference to thefollowing description and the accompanying drawings in which:

FIGURES 1(ae) illustrate a preferred method of preparing anon-conductive substrate;

FIGURES 2(ad) illustrate a preferred embodiment of the invention and themethod of construction thereof;

FIGURES 3(a-b) illustrate a non-destructive readout element and theplated circuitry customarily used in the invention; and

FIGURES 4(a-c) illustrate the invention incorporated in simplifiedmemory circuitry.

In reference to FIGURES 1(a-e), a substrate is shown in FIGURE 1(a) cladwith layers 12 and 12 on each side. The substrate 10 may consist of aconductive material (such as copper or aluminum), a non-conductivematerial (such as glass, ceramic, plastic, epoxyglass) or a materialhaving a non-conductive surface (such as hard anodized aluminum orporcelainized soft iron), the choice thereof being determined by thestrength of the material, its cost and, in this preferred embodiment,its ability to be photochemically drilled as described hereafter. Forthe purpose of this description only and not as a limitation on theinvention, substrate 10 shall be assumed to be non-conductive, anon-conductive substrate being defined as one being non-conductivethroughout or having a non-conductive surface. Although, in thisembodiment, the substrate 10 has holes photochemically drilled in it,this technique should not be considered the sole one for the purpose ofthis invention. Any technique which forms a surface that is smoothenough so that the magnetic characteristics of a magnetic material whichis plated thereon, as described more fully hereafter, are independent ofthe surface structure of the substrate 10 is sufiicient for purposes ofthis invention. For example, the holes may be molded, punched, ordrilled through the substrate 10, and then an additional layer of amaterial having a glassy surface, such as epoxy resin in the case of anepoxy-glass substrate, may be placed over the substrate 10 and on thewalls of the holes formed therethrough to provide a smoother base onwhich to plate the magnetic material.

As illustrated in FIGURE 1(b), the layers 12 and 12' are covered with astandard photo-resist material 14 and 14, such as Kodak photo-resist,made by Eastman Kodak Company, which when exposed to ultraviolet lightthrough a mask becomes selectively insoluble. The photo-resist material14 and 14' is then exposed to ultraviolet light through mask 16 and 16'to form a precisely aligned front and back hole pattern on thephoto-resist material 14 and 14, which material is subsequentlydeveloped and removed leaving an exposed hole pattern on the layers 12and 12'. The exposed areas of the layers 12 and 12 are chemicallyremoved using, in the case of a copper layer, a forced fine-mist sprayof ferric chloride as an etchant to form uniform round holes in thelayers 12 and 12; in addition, the substrate 10 may be mounted on arotary turntable so that any undercutting action of the etchant iscarefully controlled due to the uniform distribution of the etchant. Thelayers 12 and 12 may be composed of any material which is impervious toany chemical etch which may be used on substrate 10, but which itselfcan be etched by the standard photo-resist techniques described above;it should be noted that if the photo-resist material itself isimpervious to the chemical etch used on the substrate 10, as in the caseof Kodak photo-resist placed on a copper substrate, the photo-resistmaterial 14 and 14' may be substituted for the layers 12 and 12' and theinitial etching step eliminated. FIG- URE 1(0) shows the substrate 10subsequently exposed on both sides through the carefully controlled holepattern 13. The substrate 10 is then subjected to a suitable etchant,such as a mixture of hydrofluoric and concentrated sulphuric acid in thecase of epoxy-glass, and a hole pattern 18 is etched through thesubstrate 10, as shown in FIGURE 1(d). It should be noted that the holepattern 18 may be obtained, at the expense of larger holes, by etchingthrough only one of the layers 12 and 12 and keeping the other layerintact until complete removal is desired. The size, uniformity,roundness, and surface characteristics .of the holes may be selectivelycontrolled by the choice of etchant formulation, temperature, andemersion time. In addition, the use of ultrasonic agitation during theetching process has proved to be extremely valuable in keeping a properamount of unspent etchant in the small holes formed in the substrate 10,thus insuring uniform etching and relatively perpendicular walls of theholes (to the surface of the substrate 10). The layers 12 and 12' arethen removed, as seen in FIGURE 1(e), leaving the substrate 10 with thehole pattern 18 in a form suitable for use as the base upon which toplate the magnetic memory array.

In FIGURE 2(a), the substrate 10 and the holes therein are shown coatedwith a conductive layer 20, such as copper, nickel, or a magnetic alloy;if the substrate 10 is non-conductive (as previously assumed), theconductive layer 20 may be deposited, for example, by an electrolessplating technique. Since, as state previously, it is desired that themagnetic properties of a plated magnetic material be independent of thesurface structure of the substrate 10, it may be desirable toelectroplate a second conductive surface on the substrate 10, since thesurface characteristics of an electro-plated material may be morecarefully controlled. Moreover, if the surface of the substrate 10 issufiiciently smooth, the magnetic material may be electrolesslydeposited (or electro-plated if substrate 10 is conductive) directlythereon using, for example, a hypophosphite reduction of nickel andcobalt. In this embodiment, however, the substrate 10 and the conductivelayer 20 are then electro-plated with a magnetic material 22, each asPerselloy Ni-20 Fe), to produce the configuration shown in FIGURE 2(b).Ultrasonic agitation may be used during the electroplating of themagnetic material 22 on the conductive layer 20, since it has beenexperimentally found that the use thereof improves the uniformity of themagnetic material 22 in the hole pattern 18 and in the individual holesand assists in controlling the cell size of the individual grains of themagnetic material 22, the orientation of the magnetization vectors inthe material 22, and the anisotropy of the magnetic material 22.Although the geometric configuration of the magnetic material 22 platedin the hole pattern 18 produces a circumferential easy direction ofmagnetization in each hole of the hole pattern 18 and thus naturallyorients the magnetization vectors of the magnetic material 22, thisnatural magnetic orientation of the magnetic material 22 may be enhancedduring the electroplating process by imposition of a rotating magneticfield (H), with the plane of rotation coinciding with the plane of thesubstrate 10.

Portions of the magnetic material 22 and the conductive layer 20 arethen chemically etched from the surface of the substrate usingphoto-resist techniques so that only the material in the hole pattern 18remains, as shown in FIGURE 2 (c), to form a matrix of plated magnetictoroids. Although this technique is preferred, the magnetic material 22may be selectively plated on the conductive layer 20, for example, bypreviously etching the desired pattern on the conductive layer 20 usingphoto-resist techniques and electro-plating the magnetic material 22thereon. Moreover, although a matrix of plated magnetic toroids has beenshown, the magnetic material 22 in the individual holes of the holepattern 18 can be connected to the magnetic material 22 in any otherhole or combination of holes by suitable masking techniques to form anydesired configuration of connect, plated magnetic toroids. Asillustrated in FIGURE 2(d), the substrate 10 and the magnetic material22 are then coated with a layer of insulating material 24, and a desiredpattern of metallic conductors 26 is laid down on top of the insulatingmaterial 24, across the surface of .the substrate 10, and through thehole pattern 18. Although the insulating material 24 between themagnetic material 22 and the conductors 26 is desirable, for example, toprevent eddy currents in the magnetic material 22 (caused by currentflowing therethrough), it is not essential for the operation of theinvention. Moreover, as described more fully in relation to FIGURES3(ai-b), metallic conductors, such as conductors 26, may be formedbefore the magnetic material is deposited.

FIGURE 4(a) illustrates a plated magnetic toroid incorporated in asimplified memory circuit and operating in a destructive readout mode ofoperation (DRO). Substrate 10 is shown with magnetic material 22 platedon the walls of a hole therein to form the plated magnetic toroid; leads32, 34, and 36 are threaded therethrough and are connected to writedriver 38, interrogate driver 40, and a sensing circuit 42 respectively.In the DRO mode of operation, write driver 38 generates acircumferential magnetic field which orients the magnetization vectorsof the plated magnetic toroid clockwise or counterclockwise; interrogatedriver 40 generates a circumferential magnetic field which reverses theorientation of any magnetization vectors antiparallel thereto; andsensing circuit 42 responds to any changes in the orientation of themagnetization vectors in the plated magnetic toroid. All of the drivingand sensing elements are standard items commonly used in the art, while,in the practice of the invention, the leads would be plated on thesubstrate 10 and through the holes, as previously described.

Although the above matrix of plated magnetic holes is commonly used insuch a destructive readout mode of operation (DRO), for a great manyapplications a nondestructive'readout mode of operation (NDRO) ispreferred. The plating techniques described in conjunction with FIGURES2(a-d) can be adapted to fabricate the structure shown in FIGURES3(a-b). A metallic strip 28 is placed between holes 18(a) and 18(b); themetallic strip 28 may be plated on the substrate 10, or it may be etchedfrom one of the metallic layers 12 and 12, or it may be made integralwith the substrate 10 during its fabrication. The magnetic material 22is then plated through the holes 18(a) and 18(b) and across thesubstrate 10 (and over the metallic strip 28) to join correspondingedges of the plated magnetic toroids 22(a) and 22(b) to form the NDROelement 30 shown in simplified form in FIG- URE 3(b). It should be notedthat such an element may also be fabricated by other techniques, such asmolding, or compressing and sintering a powder. In addition, themetallic strip 28 may be insulated from the magnetic material 22 by alayer of insulating material, such as layer 24 in FIGURE 2(d), but suchinsulation is not necessary for the operation of the invention; if,however, substrate 10 is conductive, then metalic strip 28 must beinsulated from the substrate 10 itself. Although the rotating magneticfield used during the plating of the magnetic material 22 enhances themagnetic orientation of the plated magnetic toroids (designated as 22)in the circumferenetial direction, the connecting magnetic materal(designated as 22") remains isotropic. The remaining metallic leads 26'and 26" are then plated over the substrate 10 and through the hole 18a,1812, as previously described, the metallic leads 26 and 26 beingelectrically insulated from each other by a layer of insulating material(not shown).

Information is written into the NDRO element by 30 by a pulse applied tolead 26" (by write driver 38) which orients the magnetization vectors ofthe plated magnetic toroids 22a and 22b along one of the twocircumferential easy directions of magnetization. It should be notedthat a closed flux path, orthogonal to the closed flux paths of theplated magnetic toroids 22a and 22b, is formed by the isotropic magneticmaterial 22" and the anisotropic magnetic material in the edges of theplated magnetic toroids 22a and 22b nearest the center of the NDROelement 30. Because this formed closed flux path contains part of theanisotropic magnetic material of the plated magnetic toroids 22a and22b, the metallic strip 28, surrounded by the formed closed flux path,is capable when pulsed of reorienting a portion of the magnetizationvectors of the plated magnetic toroids 22a and 22b; that is, a portionof the magnetization vectors circumferentially directed in the platedmagnetic toroids 22a and 22b will be rotated into the hard direction ofmagnetization of the plated magnetic toroids 22a and 22b along theformed closed flux path described above. If an interrogate signal isthen applied to metallic strip 28 (by interrogate driver 40), themagnetization vectors in the region common to the plated magnetictoroids 22a and 22b and the formed closed flux path become reoriented,causing a decrease in the magnetic flux linked by metallic lead 26'. Asa result, an output pulse is obtained (on metallic lead 26') with itspolarity dependent on the initial magnetic orientation of the platedmagnetic toroids 22a and 22b. The magnetic anisotropy of the platedmagnetic toroids 22a and 22b reorients the magnetization vectors thereofto their initial state when the interrogate pulse is removed. Theinformation content of the NDRO element 30 is thus represented by abipolar output whose polarity, as before, depends on the initialmagnetic orientation of the plated magnetic toroids 22a and 22b.

FIGURE 4(b) illustrates the NDRO element 30, formed from magneticmaterial 22 plated on substrate 10, integrated in a simplified memorycircuit. Lead 26" is connected to write driver 38, metallic strip 28 isconnected through lead 28' to interrogated driver 40, and lead 26' isconnected to sensing circuit 42' All of these elements operate in themode herein described to produce a bipolar output of opposite polarity.It should be noted that since the closed flux paths of the platedmagnetic toroids 22a and 22b, which lie in the plane of the substrate10, are joined only by the isotropic connecting magnetic material 22",the toroids 22a and 22b act substantially independent of one another asfar as magnetic coupling effects are concerned. As such, the circuity inFIGURE 4(b) can be modified to store two bits of information by theaddition of a second write drive and a second sensing circuit; each oneof the two write drivers and sensing circuits coacts with acorresponding one of toroids 22a and 22b to write and sense information.This modified circuit has the additional advantage that both bits ofinformation can be simultaneously read-out by the application of asingle interrogate signal by interrogate driver 40.

While readout pulses of opposite polarity, as described above, aresatisfactory for many type of logic circuitry, it is often desirable tohave an output in a N'DRO mode of operation which has a value of or 1depending on whether the magnetic field of the interrogate pulse isparallel or antiparallel to the magnetic orientation of the memoryelement. FIGURE 4(0) illustrates the NDRO element, described inconjunction with FIGURES 3 (a-b), coupled to memory circuitry adaptedfor such a mode of operation. Metallic lead 26 is connected to writedriver 38, metallic lead 26' is connected to interrogate driver 40, andmetallic strip 28 is connected through lead 28 to sensing circuit 42 andbias source 44. It should be noted that the metallic strip 23, which nowhas a small DC. bias applied to it by bias source 44, is used forsensing the magnetic orientation of the plated magnetic toroids 22a and22'b. If the magnetic field of the metallic lead 26', caused byinterrogate driver 40, is antiparallel to the direction of magnetizationof the plated magnetic toroids 22'a and 22b, the magnetization vectorsin the edges of of the plated magnetic toroids 22'a and 22']; nearestthe center of the NDRO element 30 can be easily rotated since thevarious forces constraining the magnetization vectors to be along theeasy direction of magnetization are largely reduced. The magnetic fieldof the DC bias causes such uncoupled magnetization vectors to rotate inthe direction of such magnetic field and thus causes a positive currentto be generated in the metallic strip 28. Upon removal of theinterrogate pulse, the magnetization vectors in the edges of the platedmagnetic toroids 22'a and 22'!) return to their initial state because ofthe magnetic aniso tropy of the plated magnetic torids 22'a and 22b.Generally speaking then, if the magnetic field of the inter rogate pulseis of a polarity opposite to the magnetic orientation of the platedmagnetic toroids 22a and 22']; representing the information written inthe NDRO element 30, a bipolar output is obtained. If, however, themagnetic field of the interrogate pulse is parallel to the magneticorientation of the plated magnetic toroids 22a and 22/17, themagnetization vectors in the aforementioned edges rotate only a smallamount into the direction of magnetization of the plated magnetictoroids 22a and 221), and an output is detected which is a factor of totimes less in magnitude than the above-mentioned bipolar output. Thismode of operation thus yields the desired output values of 0 or 1depending on whether the magnetic field of the interrogate pulse isparallel or antiparallel to the magnetic orientation of the memoryelement.

Having thus described the invention, it is obvious that numerousmodifications and departures may be made by those skilled in the art;thus, the invention is to be construed as limited only by the spirit andscope of the appended claims.

What is claimed is:

1. A magnetic memory element comprising:

a substrate having at least first and second spaced-apart aperturestherethrough;

a layer of magnetizable material affixed to the walls of said first andsecond apertures to form first and second circumferential closed fluxpaths, respectively;

a layer of magnetic material joining the corresponding edges of adjacentportions of said first and second flux paths to form a third closed fluxpath angularly oriented to said first and second flux paths;

means, coupled to at least one of said first and second flux paths, forWriting information into said mem- Cal ory element, said writing meansincluding means for setting said least one flux path into a first orsecond circumferential remanent magnetic state;

interrogation means, coupled to at least one of said first and secondflux paths, for temporarily applying a magnetic field along a selectedone of first and second circumferential directions;

bias means, coupled to said third flux path, for applying a magneticfield thereto along a third direction angularly oriented to said firstand second circumferential directions; and

sensing means, coupled to said third flux path for senssing the changein flux in said third direction during the application of saidinterrogation field.

2. The magnetic memory element of claim 1 wherein said first and secondflux paths have substantially parallel axes, and said third flux path issubstantially orthogonal to said first and second flux paths.

3. The magnetic memory element of claim 1 wherein said first and secondflux paths are formed of anisotropic magnetic material having the easydirection of magnetization along said first and second circumferentialdirections.

4. The magnetic memory element of claim 3 wherein said layer of magneticmaterial joining said first and second flux paths comprises isotropicmagnetic material.

5. The magnetic memory element of claim 4 wherein said third flux pathhas portions thereof common to said first and second flux paths, andsaid third direction is substantially parallel to the hard direction ofmagnetization of said common portions.

6. The magnetic memory element of claim 1 wherein said sensing meansincludes means for generating a first bipolar output signal when saidinterrogation field is antiparallel to the circumferential remanentmagnetic state established by said writing means, and a second bipolaroutput signal when said interrogation field is parallel to thecircumferentialremanent magnetic state established by said writingmeans; said first signal being of substantially greater amplitude thansaid second signal.

7. The magnetic memory element of claim 1 wherein said Writing means andsaid interrogation means are coupled to said first and second fiuxpaths.

8. The magnetic memory element of claim 1 wherein said interrogationmeans and said writing means are each coupled to at least one of saidfirst and second flux paths by one or more layers of conductive materialplated on said substrate adjacent said layer of magnetic material, andsaid sensing and bias means are coupled to said third fluX path by aprinted conductive lead formed on said substrate through said third fluxpath.

9. The magnetic memory element of claim 1 wherein said apertures formhollow cylinder shaped structures, and a layer of glassy material isaffixed to the walls of said first and second apertures beneath saidlayer of magnetizable material.

References Cited UNITED STATES PATENTS 3,000,004 9/1961 Weller 3401743,060,321 10/1962 =Woods 30788 3,061,820 10/1962 Wanlass 340-1743,305,845 2/1967 Grace et al. 340-174 STANLEY M. URYNOWICZ, JR., PrimaryExaminer U.S. Cl. X.R. 29-604

